Unsteady Evaporation of Water from Wire Mesh Structures at Sub-Atmospheric Pressures

Evaporator development for adsorption heat pumps and chillers with water as refrigerant is a challenging task since the required sub-atmospheric pressure level usually impedes efficient evaporation. A promising concept for one-chamber adsorption modules is a combined evaporator-condenser heat exchanger in cyclic operation with external capillary structure. In this work the interplay between dewetting and evaporation dynamics of an innovative copper wire mesh structure for such an evaporator-condenser is analyzed by means of unsteady evaporation measurements and simulations with a simple resistance-capacitance model. The results reveal that for large and medium characteristic pore sizes (2.5 mm and 0.8 mm) a dewetting pattern in the shape of a receding front is formed. In contrast, a smaller pore size (0.375 mm) apparently promotes a cluster-like dewetting pattern. The fine-porous sample reaches overall effective heat transfer coefficients of up to 23 ... 28 kW/(m(2)K) which makes the wire mesh structures a promising approach for efficient evaporation.